As such grass trimmers as of the present invention, there are already provided inventions mentioned in the publications of Japanese patent publications Nos. 22484/1984 (U.S. Pat. No. 4,104,796) and 53562/1985 (U.S. Pat. No. 4,584,771).
The former invention is generally called a full automatic type wherein, for example, when a nylon cord is made short by wear or break, the load on a prime mover will reduce but, on the contrary, the rotating speed will increase and, as a result, a sliding member provided within a head will be moved toward the outer periphery of the head by the action of an increased centrifugal force, the connection of the driving shaft side with the spool side will be released by the action of the above mentioned sliding member, the spool will be made free and will be pulled by the centrifugal force and the nylon cord will be payed out. When the nylon cord becomes long as predetermined, the load on the prime mover will increase but, on the contrary, the rotating speed will reduce and, as a result, the sliding member within the head will be returned to a predetermined position by a spring, the driving shaft side will be connected with the spool side and paying out the nylon cord will be stopped.
In case the operation is normal, this full automatic type will be very convenient but, in case the nylon cord becomes very short due to break or the like, even if the rotation of the engine is increased by operating a throttle lever, no tension by the centrifugal force will act on the nylon cord and the nylon cord will not be payed out or will be payed out while the operator does not know and therefore, in case the amount payed out once is large, a large shock and reaction will be caused to the operator.
In case the above mentioned automatic paying out is not made, in order to release the connection of the driving shaft side with the spool side, such disassembling operation as removing the spool has been necessary.
The above mentioned latter invention is generally called a semi-automatic type wherein, when the spool side wound with the nylon cord is reciprocated by a predetermined stroke in the axial direction of the driving shaft with respect to the driving shaft side, the nylon cord will be payed out by repeating the release and connection of the rotation around the above mentioned shaft in some range between the above mentioned spool side and driving shaft side, therefore, if the reciprocation of the spool is repeated while pulling the nylon cord, the nylon cord will be able to be pulled even by hand and, even in case the nylon cord becomes very short due to break or the like, such disassembling as in the full automatic type will not be required.
The present invention relates to the above mentioned latter invention, that is, the structure of the head of the semi-automatic type.
However, even in the above mentioned conventional semi-automatic type head, that is, the invention mentioned in the publication of the Japanese patent publication No. 53562/1985, in case the nylon cord breaks and comes, for example, into a housing, a machine bolt shown there must be removed and further a filament holding member (spool), first and second engaging means and cover must be disassembled by using tools. Further, this has been the same also in case the nylon cord has become none and must be supplemented.
Also, the nylon cord wound on the spool does not fit the spool and always tends to return to be straight and particularly, when the spool is to be mounted, the nylon cord will be naturally released and will require much trouble to handle.